chore: add non-bundled standard lib gems for ruby 3.4

Author: Justintime50

easypost.gemspec

@@ -21,8 +21,12 @@ Gem::Specification.new do |spec|
   spec.require_paths = ['lib']
   spec.required_ruby_version = '>= 2.6'
 
+  spec.add_development_dependency 'abbrev', '~> 0.1'
+  spec.add_development_dependency 'bigdecimal', '~> 3'
   spec.add_development_dependency 'brakeman', '~> 5.4'
   spec.add_development_dependency 'faraday', '~> 2.7.5' # used for integration tests
+  spec.add_development_dependency 'logger', '~> 1'
+  spec.add_development_dependency 'ostruct', '~> 0.6'
   spec.add_development_dependency 'pry', '~> 0.14'
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rdoc', '~> 6.9'